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Creating an interesting stutter video effect with the undersample rate

by Gary Rebholz


As an editor, you most likely look for some sort of special effect to apply to your video clips every now and then. Of course, filters and video effects come immediately to mind and the Vegas line of software offers a long list of these. However, for a different and somewhat unique effect that you might not have ever used, change the undersample rate for selected video events on your timeline. This creates an interesting effect in the right situations. In this article, we'll talk about how to set the undersample rate in Vegas Pro software.


First, find a clip that can work well for an undersample rate change. Of course, you can use any clip, but as you'll see as you start experimenting, it works best on clips with fast motion, like a bicycle race, zooming cars, or perhaps a clip from a music video that has good motion. Add your clip to the timeline. Play the clip and note that if it was a well shot clip, you can see that the motion is nice and smooth as it plays back at something like 24, 25, or 30 frames per second depending upon your camera settings. (This, of course, assumes that your computer system can handle playing the clip back at full frame rate in the Vegas Pro preview window.)


With the undersample rate setting, we can cause the clip to play back in a choppier manner, giving the motion a stuttering or strobe-like effect. To set the undersample rate, right-click the video event and choose Properties from the menu. In Figure 1 you can see that the Undersample rate field shows the current rate setting. By default, all events come in with a value of 1.0 as the undersample rate setting. That makes sense because by default all clips play at one times their normal frame rate — that is, they play at their normal frame rate. To the right of the rate setting you see the framerate at which the clip will play back. Figure 1 shows that I'm using NTSC footage that was shot at 29.970 frames per second.


Figure 1

The Properties dialog box shows the event's default Undersample rate of 1.0 as well as the playback rate of 29.970.


Use the Undersample rate spinner control to lower the rate from its normal setting of 1.0. Notice that as you do, the frame rate indication drops too. What's going on here? Well, let's take an easy case to figure the math on. Drop the Undersample rate setting to .50. You can use the spinner controls or type the value into the Undersample rate field directly.


Figure 2 shows that with an undersample rate .5, the frame rate drops to 14.985 fps. This means that now the video in this event will play half the number of frames as usual. It also means then that each frame will stay on screen for twice as long as usual so that the video lasts for as long as it normally would. Remember; you're not creating slow motion here (for that, use the Playback rate setting). Instead, you're simply telling Vegas Pro software to play half the number of frames in the same amount of time, thus increasing the time that each frame must be shown on screen before going to the next frame.


Figure 2

With an undersample rate of .5, Vegas Pro software will play half the number of frames and make each one last twice as long to create a stuttering playback effect.


Click OK to close the Properties window, then play your project. As I said, dropping the undersample rate does not create slow motion. Instead, it creates motion that happens in regular time, but gives a more stuttering picture. You can see therefore why this has more of an effect on video with lots of motion. As an object moves across the picture, its motion is jerkier than at normal playback. The lower you drop the undersample rate, the more pronounced the stuttering effect.


Try a few different settings. Drop the undersample rate down to its lowest possible level of .100 and then play your project again to see how that affects the video. This can almost give the impression that you're not watching video at all, rather a series of still images played one after another.


Now you can get creative. If your video is driven by a music bed, try to dial in an undersample rate that feels like it causes the video to strobe or stutter in the rhythm of the music. Add a Light Rays filter or some other video effect to the event and see what that does to the picture. Try increasing the contrast on the clip with the Brightness and Contrast filter and see what you get.


If you really want to slow down the rate at which the frames change, drop the playback rate setting too and create slow motion. With both the playback rate and the undersample rate dropped to their lowest possible values, you really get the sense that you're watching a series of still images instead of video. And you can use the playback rate setting to really dial into the rhythm of the music in your video if you can't get there with just the undersample rate setting.


The point is, just try some different things and see what you can make happen.


Most of the time, we border on obsession with getting the smoothest motion possible on our videos. And with good reason. But once in a while, when you need something just a bit different, reach for the undersample rate setting and add some jerk to that smooth video. You might be surprised by what you come up with and the affect it has on your final video production.


If you want to watch as I go through each of the steps in this article, check for the next video in the free video tutorials hosted by Les Stroud. Also check out all of our other free training videos and other training resources at http://www.sonycreativesoftware.com/training.



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